The present invention relates to a magnetic memory device. More particularly, it relates to a magnetic memory device having a recording layer.
The magnetoresistive (MR) effect is a phenomenon that the electric resistance is changed by applying a magnetic field to a magnetic substance, and is utilized for a magnetic field sensor, a magnetic head, and the like. Particularly, as giant magnetoresistance (GMR) effect materials exhibiting a very large magnetoresistive effect, artificial lattice films of Fe/Cr, Co/Cu, and the like are introduced in Non-Patent Documents 1 and 2.
Whereas, there is proposed a magnetoresistive effect element using a lamination structure comprised of ferromagnetic layer/non-magnetic layer/ferromagnetic layer/antiferromagnetic layer having a non-magnetic metal layer which is thick to such a degree as to eliminate the exchange coupling action between the ferromagnetic layers. In this element, the ferromagnetic layer and the antiferromagnetic layer are exchange coupled to each other. Thus, the magnetic moment of the ferromagnetic layer is fixed, so that only the spin of the other ferromagnetic layer can be reversed with ease in the external magnetic field. This is an element known as a so-called spin valve film. With this element, the exchange coupling between the two ferromagnetic layers is weak, and hence the spin can be reversed in a small magnetic field. For this reason, the spin valve film can provide a magnetoresistive element with a higher sensitivity than that of the exchange coupled film. As the antiferromagnetic substance, FeMn, IrMn, PtMn, or the like is used. In the spin valve film, an electric current is made to flow in the film in-plane direction for use. Thus, the spin valve film is used for a reproducing head for high density magnetic recording because of its feature as described above.
On the other hand, Non-Patent Document 3 discloses as follows: Use of the perpendicular magnetoresistive effect of making an electric current flow in the direction perpendicular to the film plane provides a further larger magnetoresistive effect.
Further, Non-Patent Document 4 also discloses a tunneling magnetoresistive (TMR) effect due to the ferromagnetic tunnel junction. The tunneling magnetoresistance is produced by using the following: in a three-layer film including ferromagnetic layer/insulation layer/ferromagnetic layer, the spins of the two ferromagnetic layers are caused to be parallel or anti-parallel to each other by the external magnetic field, resulting in a difference in magnitude between the tunnel currents in the direction perpendicular to the film plane.
In recent years, the studies on use of GMR and TMR elements for a nonvolatile magnetic memory semiconductor device (MRAM: magnetic random access memory) have been shown in, for example, Non-Patent Documents 5 to 7.
In this case, studies have been made on a pseudo-spin valve element in which a non-magnetic metal layer is sandwiched between two ferromagnetic layers having different coercive forces, and a ferromagnetic tunneling effect element. When these elements are used for an MRAM, these elements are arranged in a matrix. Thus, an electric current is made to flow to an additionally provided wire, so that a magnetic field is applied thereto. As a result, the two magnetic layers forming each element are controlled to be parallel or anti-parallel to each other, so that “1” or “0” are recorded. Reading is performed by using the GMR and TMR effects.
For an MRAM, the use of the TMR effect results in a lower power consumption than the use of the GMR effect, and hence, use of the TMR element has been mainly studied. With an MRAM using a TMR element, the MR ratio is as large as 20% or more at room temperature, and the resistance at the tunnel junction is large. Therefore, a larger output voltage can be obtained. Whereas, with the MRAM using a TMR element, spin reversal is not required to be performed for reading, so that reading is possible with the less current. For this reason, the MRAM using a TMR element has been expected as a low power consumption type nonvolatile semiconductor memory device capable of high-speed writing/reading.
For the write operation of the MRAM, it is desired that the magnetic characteristics of the ferromagnetic layers in the TMR element are controlled. Specifically, there are demands for a technology of controlling the relative magnetization directions of two ferromagnetic layers interposing a non-magnetic layer are controlled to be parallel/anti-parallel, and a technology of causing the magnetization reversal of one magnetic layer in a desired cell with reliability and efficiency. The technologies of controlling the relative magnetization directions of two ferromagnetic layers interposing a non-magnetic layer to be uniformly parallel/anti-parallel in the film plane by using two crossing wires are disclosed in, for example, Patent Documents 1, 3, 4, and 7.
Whereas, for an MRAM, when cell size reduction is carried out for higher integration, the reversing magnetic field increases due to the demagnetizing field depending upon the size in the direction of the film plane of the magnetic layer. As a result, a large magnetic field is required for writing, and the power consumption also increases. For this reason, as shown in the Patent Documents 2, 5, 6, and 7, there are proposed technologies whereby the shape of the ferromagnetic layer is optimized, thereby to facilitate magnetization reversal.
[Non-Patent Document 1] D. H. Mosca et al., “Oscillatory interlayer coupling and giant magnetoresistance in Co/Cu multilayers”, Journal of Magnetism and Magnetic Materials 94 (1991) pp. L1-L5
[Non-Patent Document 2] S. S. P. Parkin et al., “Oscillatory Magnetic Exchange Coupling through Thin Copper Layers”, Physical Review Letters, vol. 66, No. 16, 22 Apr. 1991, pp. 2152-2155
[Non-Patent Document 3] W. P. Pratt et al., “Perpendicular Giant Magnetoresistances of Ag/Co Multilayers”, Physical Review Letters, vol. 66, No. 23, 10 Jun. 1991, pp. 3060-3063
[Non-Patent Document 4] T. Miyazaki et al., “Giant magnetic tunneling effect in Fe/Al203/Fe junction”, Journal of Magnetism and Magnetic Materials 139 (1995), pp. L231-L234
[Non-Patent Document 5] S. Tehrani et al., “High density submicron magnetoresistive random access memory (invited)”, Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5822-5827
[Non-Patent Document 6] S. S. P. Parkin et al., “Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory (invited)”, Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5828-5833
[Non-Patent Document 7] ISSCC 2001 Dig of Tech. Papers, p. 122
[Patent Document 1] Japanese Unexamined Patent Publication No. Hei 11 (1999)-273337
[Patent Document 2] Japanese Unexamined Patent Publication No. 2002-280637
[Patent Document 3] Japanese Unexamined Patent Publication No. 2000-353791
[Patent Document 4] U.S. Pat. No. 6,005,800
[Patent Document 5] Japanese Unexamined Patent Publication No. 2004-296858
[Patent Document 6] U.S. Pat. No. 6,570,783
[Patent Document 7] Japanese Unexamined Patent Publication No. 2005-310971